The present invention relates to centrifugal pumps, and more particularly to a novel seal for providing liquid flow isolation between the interior of the pump and the exterior through the pump shaft opening. The invention is primarily adaptable for use in connection with centrifugal pumps having a vertical drive shaft orientation, including one or more series-connected stages of pumping elements for developing elevated pressure and flow conditions.
The use of series-connected impeller pumps for developing increasing pressure levels is well-known in the art, including the use of such pumps in connection with a common drive shaft. One such pump is manufactured by the assignee of the present invention under the model name "Imperial" centrifugal pump, which utilizes from four to twelve impeller pumps ganged together on a single drive shaft and connected to an electrical drive motor. Each of the impeller stages are series-connected to provide successively increasing pressures and relatively high flow rates of viscous liquids. The impeller stages are assembled in stacked relationship on a pump stand, with a vertical drive shaft extending from the bottom stage through the topmost stage and terminating in a housing mounted on the pump stand above all of the stages. An electric drive motor is mounted on top the housing, and a mechanical coupling link is provided between the drive motor and the drive shaft. An inlet connection is provided into the bottom pumping stage, and internal passages couple successive stages together in series flow fashion. The topmost stage is fluid coupled into an outlet housing, and pumped liquid is delivered from this housing to various conduits.
In an industrial plant setting, a pump of the type described herein is typically placed near a large volume container which may hold paint, oils, or other liquid materials, and the pump outlet is connected to a conduit delivery system which may be piped over fairly long distances within the industrial plant. These pumping systems are typically operated over long periods of time, and may in certain instances be operated twenty-four hours per day indefinitely until a maintenance problem develops within the pump. The most typical maintenance problem is a leakage problem caused when the various shaft seals began to wear away, which initially results in a fairly small amount of leakage which builds-up over time until the leaking pump liquid accumulates over the area around the pump. When this occurs the pump delivery system must be shut down for maintenance and repair.
Since these pumps typically operate over long periods of time and are unattended, it is extremely important that a high degree of reliability be built into the pump. Since the most frequent maintenance problem arises out of leakage through shaft seals, great care is usually taken to design effective seals which will operate over extended time periods. The most frequent cause of shaft seal leakage results from over heating caused by friction, and it is therefore extremely important to design such seals to operate with as little frictional heat build-up as possible.